Integration of ferromagnetic films with ultrathin insulating film using atomic layer deposition

ABSTRACT

A technique to form an ultrathin dielectric layer over a ferromagnetic layer by atomic layer deposition.

RELATED APPLICATION

This application claims priority from U.S. Provisional Pat. App. Ser.No. 60/239,614 entitled “Integration of Ferromagnetic Films WithUltrathin Insulating Films for Fabrication of Tunneling Devices UsingAtomic Layer Deposition” filed Oct. 11, 2000.

FIELD OF THE INVENTION

The present invention relates generally to thin film depositiontechnology pertaining to magnetic storage devices and, moreparticularly, to a process of manufacturingferromagnetic-insulator-ferromagnetic tunneling devices in which atomiclayer deposition is used to prepare and form the insulator film.

BACKGROUND OF THE RELATED ART

In the manufacture of magnetic storage devices, deposition techniquesfor thin films of various pure and compound materials have beendeveloped to achieve the deposition of such thin films. Recentlyemerging spin polarized tunneling devices inferromagnetic-insulator-ferromagnetic (FM/I/FM) tunneling junctionsindicates that this technology has applications for non-volatilemagnetic memory elements or storage media.

In the manufacture of FM/I/FM materials, ferromagnetic metallicelectrodes for these devices may be deposited using available PhysicalVapor Deposition (PVD) processes. Although tunneling devices can bemanufactured using the Physical Vapor Deposition process, a number ofacute disadvantages are noted with this technique. For example, an ultrathin continuous and high quality insulating (dielectric) film, having athickness in the range of 5-20 Å, is difficult to achieve with PVD,since discontinuities result with PVD nucleation processes. Furthermore,oxidation of ferromagnetic materials at the FM/I interface may occurduring reactive sputtering process from energetic and atomic oxygen andsuch oxidation is undesirable, since such oxidation at the FM/Iinterface may be detrimental to device performance. Given thedifficulties to deposit continuous oxide films with PVD and given theunavoidable effects of substrate oxidation an alternative PVD solutionhas implemented sputtering evaporation or molecular beam deposition ofultrathin metal films, such as Aluminum, followed successfully by an insitu oxidation. However, this method may not, so far, produce adequateresults. Accordingly, standard PVD techniques may have difficultymeeting the deposition of insulating material (I) on ferromagneticmaterial (FM).

In the field of chemical vapor deposition (CVD), a process known asatomic layer deposition (ALD) has emerged as a different but promisingtechnique to extend the abilities of CVD. Generally, ALD is a processwherein conventional CVD processes are divided into single-monolayerdepositions, in which each separate deposition step theoretically goesto saturation at a single molecular or atomic monolayer thickness andself-terminates when the mono layer formation occurs on the surface of amaterial. Generally, in the standard CVD process the precursors are fedsimultaneously into a reactor. In an ALD process the precursors areintroduced into the reactor separately at different steps. Typically theprecursors are introduced separately by alternating the flow of theprecursor to combine with a carrier gas being introduced into thereactor while coexistence of the precursors in the reactor is maintainedby appropriately purging the reactor in between successive introductionof precursors.

For example, when ALD is used to deposit a thin film layer on a materiallayer, such as a semiconductor substrate, saturating at a singlemolecular or atomic monolayer of thickness results in a formation of apure desired film and eliminates the extra atoms that comprise themolecular precursors (or ligands). By the use of alternating precursors,ALD allows for single layer growth per cycle so that much tighterthickness controls can be exercised to deposit an ultra thin film.Additionally, ALD films may be grown with continuity with thickness thatis as thin as a monolayer (3-5 Angstroms). This capability is oneunmatched characteristic of ALD films that makes them superiorcandidates for applications that require ultrathin films such asinsulator in FM/I/FM devices.

The present invention is directed to providing an ultra thin insulation(dielectric) layer above a ferromagnetic layer by the utilization ofatomic layer deposition. Such technique may then be employed tofabricate FM/I/FM tunneling junctions, which may then fabricate magneticstorage devices. Sharp interfaces at the FM/I junctions are consideredto be important characteristic for ultimate performance of FM/I/FMtunneling junction devices. Accordingly, integration of ferromagneticbottom electrode with the insulator is an important aspect of obtaininga good FM/I junction to construct FM/I/FM devices. Current PVDtechnology implements a sequence of PVD depositions at high and ultrahigh vacuum as the leading approach for making the interface between thebottom ferromagnetic electrode and the overlying insulator material. PVDalone makes the fabrication of the insulator layer above theferromagnetic bottom electrode elusive, but especially for an insulatorwhich is oxide and contamination free.

Furthermore, an integration of PVD and CVD based technology is difficultto achieve considering that the difference between the vacuum range ofmetal PVD (which is at High Vacuum to Ultra High Vacuum) and CVD makesthe PVD-CVD integration difficult or impractical. This is especiallytrue in particular with PVD of metals and CVD of insulators. That is,depositing a bottom electrode using PVD and depositing a subsequentoverlying layer of a dielectric material using CVD is difficult.Specifically, integration of high vacuum/ultra high vacuum PVD processfor the deposition of the ferromagnetic layer and subsequent CVDdeposition of a dielectric layer to obtain an ultrathin insulator is achallenge.

In addition, in many instances the bottom electrode of the FM/I/FMneeded to be patterned. Patterning the electrode requires a process flowwith multiple steps involving photolithography and etch. These steps arebound to contaminate and oxidize the top of FM electrode andsubsequently deteriorate the performance of the final device. Therefore,a process flow that may provide means to protect the electrode duringpattern delineation is highly desired.

SUMMARY OF THE INVENTION

A method and apparatus to deposit a first ferromagnetic metal layer ontoan underlying material and to deposit a protective sacrificial layerabove the first ferromagnetic layer without exposing the firstferromagnetic layer to ambient environment. Then the ferromagneticelectrode film may be patterned, if necessary. Then, the material isplaced into an atomic layer deposition chamber. The protectivesacrificial layer is removed in situ to expose the ferromagnetic layerand without exposing the exposed ferromagnetic layer to the ambientenvironment, a dielectric layer is deposited over the firstferromagnetic layer by atomic layer deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram showing a formation of a firstferromagnetic material layer above a substrate in which an overlyingprotective sacrificial layer is also deposited to cover the firstferromagnetic layer.

FIG. 2 is a cross-sectional diagram showing the patterning and etchingof the structure of FIG. 1 to form a FM patterned electrode.

FIG. 3 is a cross-sectional diagram showing a removal of the protectivelayer of FIG. 2 and a subsequent deposition of a dielectric layer byatomic layer deposition.

FIG. 4 is a cross-sectional diagram showing a deposition of the secondferromagnetic material layer above the dielectric layer of FIG. 3 toform a FM/I/FM structure.

FIG. 5 is a cross-sectional diagram showing an alternative technique offorming another protective sacrificial layer above the dielectric layerof FIG. 3.

FIGS. 6A-B show a flow diagram for practicing one method of theinvention.

FIG. 7 is a block diagram showing an apparatus for performing ALD toform a FM/I junction of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The practice of atomic layer deposition (ALD) to deposit a film layeronto a substrate, such as a semiconductor wafer, or onto anothermaterial layer typically entails separately introducing molecularprecursors into a processing reactor chamber. The ALD technique willdeposit an ultrathin film layer atop the underlying material, whetherthe underlying material is a substrate or another material layer. Asnoted above, the growth of the ALD layer follows the chemistriesassociated with chemical vapor deposition (CVD), but the precursors areintroduced separately.

In an example ALD process for practicing the invention, the molecularprecursors are introduced into the ALD reactor separately. ALD isachieved by flowing one precursor at a time such as a metal precursorMLx that contains a metal element M, which is bonded to x number ofatomic or molecular ligands L to make a volatile molecule. The metalprecursor reaction is typically followed by inert gas purging toeliminate this precursor from the chamber prior to the subsequentintroduction of the next precursor. An ALD reaction will take place ifthe surface is prepared to react directly with the molecular precursor.For example, the MLx molecule reacts with a ligand attached to thesurface. The surface is typically prepared to include ahydrogen-containing ligand, such as AH, where A is a non-metal elementbonded to hydrogen and AH is reactive with the metal precursor. Themolecular reaction on the surface proceeds to react with the ligands onthe surface and deposit a monolayer of the metal with its passivatingligand, so that the desired reaction is noted as AH+MLx→AMLy+HL, whereHL is the exchange reaction by-product. During the reaction the initialsurface ligands AH are consumed and the surface becomes saturated with Lligands, that do not further react with the metal precursor MLxTherefore, the reaction self-saturates when all the initial ligands arereplaced with MLy species (the subscripts x and y are utilized herein todenote integers, 1, 2, 3, etc.).

After the precursor ML_(x) reacts with the surface and self-saturates toterminate the reaction, the remaining non-reacted precursor is removed,typically by allowing the carrier gas to purge the processing chamber.The second type of precursor is then introduced to restore the surfaceactivity towards the metal precursor by eliminating the L ligands andredepositing AH ligands. In this example, the second precursor iscomprised of AH_(z), A being a nonmetal element (for example oxygen,nitrogen, or sulfur) and H being hydrogen. For example H₂O, NH₃ or H₂S.The reaction ML+AH_(z)→MAH_(z-1)+HL results in a desired additionalelement A being deposited as AH terminated sights and the ligand L iseliminated as a volatile byproduct HL. This process converts the surfaceback to the AH terminated sites, which restores the surface to theinitial terminations. Again, the reaction consumes the reactive sites(this time the L terminated sites) and self-saturates when the reactivesites are entirely depleted.

The sequence of surface reactions that restores the surface to theinitial point is called the ALD deposition cycle. This deposition cycleallows the films to be layered down in equal metered sequences that aresubstantially identical in chemical kinetics, deposition per cycle,composition and thickness. Self-saturating surface reactions make ALDinsensitive to transport non-uniformity either from flow engineering orsurface topography (for example, deposition into high aspect ratiostructures).

The present invention uses the ALD process to fabricate a sharpinterface at the FM/I junction. An improved interface of the FM/Ijunction may then be utilized in fabricating a FM/I/FM tunnelingjunction device, for example, one of the above-mentioned ferromagneticmemory devices. Accordingly, an embodiment of the present invention isdescribed below in reference to the shown Figures. In the description,it is also to be noted that the illustrated embodiment forms thejunction and also takes into account the prevention of the oxidation ofthe underlying ferromagnetic metal layer. That is, after the depositionof the bottom ferromagnetic layer, a protective sacrificial layer isformed to prevent oxidation or contamination of the underlyingferromagnetic layer. The extent of such oxidation varies with thematerial, as well as the cleaning process used, but typically mayaccount for more than 10 angstroms. Accordingly, one technique forpracticing the invention attempts to reduce the thickness of thisoxidation at the FM/I interface.

In FIG. 1, one embodiment for practicing the present invention is shown.In this particular embodiment, the base material is a substrate 10 uponwhich other layers are fabricated. Furthermore, the example substrate inthis instance is a ceramic wafer utilized for manufacturing of magneticstorage devices. The example method then deposits a first (or bottom)ferromagnetic material above the substrate 10. Generally, theferromagnetic material is a thin ferromagnetic film layer 11 depositedabove the substrate 10. The ferromagnetic layer 11 is also referred toas the bottom electrode layer, since the FM layer 11 forms the bottomelectrode of a FM/I/FM device. In the described embodiment, aconventional physical vapor deposition (PVD) process deposits FM layer11. Generally the deposition is achieved in a PVD chamber having highvacuum (HV of approximately 10⁻⁵-10⁻⁸ Torr) or ultra high vacuum (UHVapproximately 10⁻⁸-<10⁻¹⁰ Torr). The HV or UHV environment of the PVDchamber minimizes substrate exposure to oxidizing or contaminatingenvironment, such as ambient environment. The PVD process may deposit avariety of materials to form the FM layer 11. Without limitation,examples of ferromagnetic materials for use in forming FM layer 11 in aPVD chamber are nickel (Ni), iron (Fe) or cobalt (Co), or alloys such asNi₈₀Fe₂₀, Co₅₀Fe₅₀ and Co₈₄Fe₁₆. The thickness of the FM layer 11 willvary depending on the particular device design desired. However, anexample structure for a FM/I/FM device may fabricate the bottomelectrode to have a thickness in the range of approximately 80 Angstromsand is approximately a 200 μm wide strip.

Subsequently, a protective sacrificial (PS) layer 12 is formed above thebottom FM layer 11. The formation of the PS layer 12 is achieved withoutexposing the FM layer 11 to oxidizing or contaminating environment, suchas the ambient environment. Generally, ambient exposure is prevented, orat least limited, by depositing the PS layer 12 by continuouslymaintaining the substrate 10 in the HV/UHV environment utilized todeposit the FM layer 11. The environment integrity may be maintained bydepositing the PS layer 12 in the same reactor chamber as used fordepositing the FM layer 11 or, alternatively, moving the substrate toanother reactor chamber of a cluster tool which maintains the sameenvironment for the various chambers in the cluster. Multiple stage PVDtools which are common in the magnetic storage industry are wellsuitable to deposit the layers 11 and 12 using 2 different sputteringtargets. In the embodiment shown, PS layer 12 is deposited also by a PVDprocess in the same PVD system.

Alternatively, another common design of these tools is to apply thefilms on multiple substrates that are mounted horizontally on a platenor vertically on a drum and are rotating continuously against asputtering source to unify the thickness on all substrates. These typesof tools typically have several cathodes (sputtering heads) which allowdeposition of different materials without ambient exposure whennecessary. Typically about 4-10 heads may be mounted on a horizontaltool and 4-6 heads on a vertical tool. These tools are utilized fordepositing the FM layer 11 and may then also deposit PS layer 12 aswell.

Generally, the protective layer 12 is comprised of a metallic material,although other material chemistry may be utilized. The composition ofthe PS layer 12 is such that a given etch chemistry will remove the PSlayer 12, but not the underlying FM layer 11. That is, the PS layer 12is selective over the underlying FM layer 11 when etched. The thicknessof the PS layer deposited by PVD will depend on other properties, buttypically a thin layer in the approximate range of 50-100 Å ensurescontinuous and pin-hole free film. A variety of materials may beselected for PS layer 12. In one technique where the FM layer iscomprised of the afore-mentioned FM materials (Ni, Fe, Co or theiralloys), materials such as tungsten (W), WNx, silicon (Si) and SiNx maybe readily used for the composition of the PS layer 12. Again, thesematerials are noted as examples and no intent is made to limit the PSlayer 12 to these materials only. It is appreciated that other metals ormetal nitrides may be readily used for the PS layer 12 as well providedthat they can selectively etched away, in situ, without affecting theunderlying FM layer.

In one example technique, a sequential integrated PVD process deposits aW-based PS layer 12 above the FM layer 11 in a continuous process in thesame reactor, simply by firing up a tungsten sputtering source when theFM source is turned off. It is appreciated that other techniques andother materials can be readily used to deposit protective layer 12. Whatis important is that the underlying FM layer 11 is not exposed to theambient (or other oxidizing or contaminating) environment. Thus, theprotective layer 12 protects layer 11 from oxidation and contamination.

Once the PS layer 12 forms a protective covering over the underlying FMlayer 11, the substrate can than be removed from the vacuum environment.Since the FM layer 11 is protected by the PS layer 12, the substratehaving the FM/PS structure may now be exposed to the ambient environmentas well as to materials and chemistries that comprise a patterndelineation process.

Referring to FIG. 2, the structure of FIG. 1 may then subsequently besubjected to a photolithography and etch to form a patterned FM/PSstructure 13. As illustrated in FIG. 2, the PS layer 12 is still presentover the FM layer 11 to ensure that the upper surface of the FM layer 11is still not subjected to the ambient environment. Accordingly, the etchprocess includes etching PS layer 12 prior to or together with etchingFM layer 11.

After completion of the pattern delineated stack 13, the substrate 10 isthen placed in an atomic layer deposition (ALD) system which is alsounder vacuum. It is appreciated that the ALD platform environment may bethe same tool as that used for the PVD deposition or, alternatively, theALD platform may be in a different tool than the tool used for the PVDprocess. Once under vacuum in the ALD platform, the protective layer 12is removed by selective etch chemistry. As was noted above, selectiveetching technique is utilized to remove the PS layer 12 without etchingthe underlying FM layer 11.

For example, if the FM layer 11 is comprised of materials resistant tofluorine etch chemistry and the PS layer 12 is comprised of W or W-basedmaterial, then isotropic fluorine etch chemistry (for example, a remoteplasma fluorine chemistry, such as NF₃) will selectively etch away thePS layer 12. That is, in a conventional etching technique, NF₃ willremove and completely etch materials that have volatile fluoridecompounds, such as WF₆. This dry chemistry etch does not remove theunderlying FM layer 11, since the fluorides of iron (Fe), nickel (Ni)and cobalt (Co) are non-volatile at typical process temperaturesapproximately below 500° C. Thus, with this selective etching techniquethe tungsten-based PS layer 12 is removed, while the underlying FM layer11 remains with its upper surface exposed. Further, the surface of theferromagnetic material of the FM layer 11 becomes terminated with atomicfluorine by the end of the PS layer 12 removal.

In one embodiment in practicing the invention, the fluorine chemistrycontinues to be applied to remove the PS layer 12, since continuedapplication of the selective etching chemistry has no adverse effects tothe exposed FM layer 11 without detriment. The ability to applyover-etching makes sacrificial layer removal relatively simple and doesnot require endpoint or tight etch control to prevent over-etching ofthe underlying FM layer 11. The plasma fluorine chemistry is followedby, for example, NH₃/H₂ plasma to remove residual fluorine and residualoxygen from the surface of the FM layer 11. This process also activatesthe surface of the exposed surface of the FM layer 11 for subsequent ALDapplication to form a continuous interface above the FM layer 11.

In this particular technique when NH₃—H₂ plasma is utilized, the surfaceof the ferromagnetic material of the FM layer 11 is tied with NH_(x)species that serve as the reactive site to initiate dielectric ALD andalso suppress oxidation by residual H₂O from the high vacuum backgroundpressure. Subsequently the NH_(x) terminated surface will be reactedwith a metal precursor to initiate ALD of the desired insulatingmaterial.

Then as shown in FIG. 3, an insulating or dielectric material layer 14is deposited by ALD. The ALD deposits a uniform and conformal layer 14over the substrate 10, including stack 13. Generally, it is desirable tohave an insulating material with a large band gap. In particular, Al₂O₃has shown desirable properties to serve as a tunneling barrier inFM/I/FM devices. However, in some instances, Al₂O₃ deposition requiresthe usage of oxygen source precursors such as H₂O. These chemicals mayconsequently attack the FM surface causing some oxidation and possibledegradation. Thus, although so far Al₂O₃ has been the most promisinginsulator candidate to practice FM/FM, insulating nitride materials mayultimately be implemented for better reliability.

However in contrast, nitride based insulators, such as AIN and Si₃N₄ maybe better suited for FM/I/FM insulators since these materials are notexpected to cause ferromagnetic material degradation. Thus, in otherembodiments nitride-based dielectric materials are utilized fordielectric layer 14. In particular, AIN has a band gap of approximately6 eV, which may facilitate better tunneling control since similartunneling currents will be achieved with thicker films allowing bettercontrol of junction properties. On the other hand, Al₂O₃ may beintegrated and may be facilitated by ALD chemistries that involve verymild oxidants such as tetraethoxysilane (TEOS), which is a very commonCVD precursor for SiO₂ deposition.

It is to be noted that in the technique described, the dielectric layer14 is deposited without subjecting the underlying FM layer 11 to ambientenvironment. Although the thickness of the dielectric layer 14 can bemade thick as desired, thickness in the approximate range of 5 to 20 Åare considered to be best and can be achieved with adequate control andcontinuity by ALD. It is to be appreciated that other chemistries may beutilized to deposit dielectric layer 14 by ALD. The deposition of thedielectric layer 14 by ALD allows for a continuous interface between theFM layer 11 and the overlying dielectric material 14. The continuousinterface is achieved since ALD precursors directly bond to thesubstrate, since films grow layer by layer and since no oxidation orcontamination occurs on the surface of the underlying FM layer 11. Thedeposition of the dielectric material by ALD also permits an ultrathinlayer of dielectric material to be formed on the FM layer 11. Theultrathin layer of the dielectric material occurs since ALD deposits oneatomic or molecular layer each cycle so that tight tolerances on filmthickness may be controlled by the use of ALD to deposit dielectriclayer 14.

Following the deposition of the ultrathin continuous insulator materialin the form of the dielectric layer 14 by the utilization of ALD, thesubstrate 10 is unloaded from the ALD platform and loaded again into thePVD platform. As shown in FIG. 4, a deposition of a second FM layer 15forms the upper or top electrode for the FM/I/FM device. The FM materialcomposition for the FM layer 15 may be the same as for the FM layer 11,although that is not necessarily required. PVD deposition of the secondFM layer 15 will be performed with little delay after atomic layerdeposition of the dielectric layer 14. The combination of the threelayers 11, 14, and 15 forms the FM/I/FM device atop substrate 10. Thus acompleted FM/I/FM stack is shown in FIG. 4.

Alternatively, as shown in FIG. 5, a second protected sacrificial layer16 may be deposited by an integrated ALD of W or WNx depositionfollowing the atomic layer deposition of dielectric layer 14. That is,after forming the dielectric layer 14, the precursor chemistry ischanged in the ALD reactor to deposit the second PS layer 16 to protectthe underlying dielectric layer 13 from ambient exposure. Two examplesare W or WNx for the material of the PS layer 16, however, othermaterials can be readily used. This PS layer 16 is used to protect theupper surface of the dielectric layer 14 during farther patterning ofthe dielectric layer, if such patterning is required.

When the PS layer 16 is utilized, the PVD system will require thenecessary chemistry to selectively remove the protective layer 16. Thus,in the W or WNx example, the PVD system will be equipped with fluorineetch capability to remove the PS layer 16. Since fluorine chemistriesare widespread and generally easy to implement, materials selected forthe PS layer 16 can be chosen so that the material will selectively etchin this flowing chemistry. In addition, both Al₂O₃ and AIN are resistantto fluorine chemistry which makes the selection of material for layer 16in favor of materials that can be etched with fluorine chemistries. Thechoice of the PS layer 16 material may also depend on other propertiesof potential materials. For example, W may be desirable to protectbottom electrode in the case that bottom electrode patterning isdesired. In addition to being fairly easy to etch with fluorinechemistries, W may be a good hard mask material with large selectivityfor ion milling which is a technique used to etch the Ni—Fe—Coferromagnetic electrodes following photolithography Tungsten may beconveniently delineated with H₂O₂ wet etch or with conventional dryfluorine chemistry to expose the underlying FM material. Subsequentlythe delineated W can be used to improve critical dimension definition byserving as an ion milling hard mask.

It is appreciated that the atomic layer deposition of Al₂O₃ can bedeployed by conventional Al(CH₃)₃ (trimethylaluminum) H₂O or AlCl₃/H₂Osequences as well as by using the above mentioned aluminum precursorswith milder oxidizers such as TEOS. AIN can be deposited by Al(CH₃)₃/NH₃or AlCl₃/NH₃ sequences. Finally, ALD can be applied to prepare AlN/Al₂O₃stacks or aluminum oxynitride insulators. It is appreciate that variousother materials and configurations can be achieved to form variousmaterial sequences. Then, as earlier shown in FIG. 4, the second FMmaterial layer 15 is deposited to form the FM/I/FM structure.

It is appreciated that in one technique to practice the invention, it isdesirable to separate ALD chambers of oxides and nitrides. Nitridechambers in particular are kept at low levels of residual H₂O and otheroxidants. If AIN or Si₃N₄ are suitable as tunneling insulators, thewhole integration and deposition process may be carried out in the samechamber. However, if insulators of oxide or oxynitrides are desired,sacrificial layer removal and surface activation may be better achievedin a separate chamber. This chamber may be used for subsequent situprotection of the insulator by a sacrificial W or WN ALD film, ifneeded.

Furthermore, it is also appreciated that in some instances ALD can beinitiated much more readily if a particular surface is pretreated priorto the ALD cycle. For example, in the ALD formation of the dielectriclayer 14, pre-treating of the surface of the underlying FM layer 11 maymake these surface terminations sights more reactive to the firstprecursor of the ALD cycle. Such surface pre-treatment to createadditional termination sites may be achieved by the introduction ofpre-treatment chemicals into the ALD reactor chamber before theprecursor is introduced.

Referring to FIGS. 6A-B, a flow diagram 20 exemplifies one embodiment ofthe base process for forming a FM/I/FM device on a ceramic wafer. Afterwafer clean (block 21), a first FM layer is deposited by PVD (block 22)followed by a PVD deposition of a PS layer (block 23), without exposingthe first FM layer to ambient or other oxidizing/contaminatingenvironment. The FM1/PS stack is patterned and etched (block 24). Next,the wafer is transported to an ALD reactor without concern for FM1oxidation, since FM1 layer is not exposed. In the ALD reactor, the PSlayer is removed (block 25), followed by dielectric (I) layer depositionby ALD (block 26). Finally, the wafer is placed back in the PVD chamberfor the PVD deposition of the second FM layer (block 27). It is to benoted that the wafer may be transferred to a different system betweenthe transition between block 26 and block 27.

An apparatus for performing ALD to practice the invention is shown inFIG. 7. An example ALD reactor apparatus 30 is shown. Reactor 30includes a processing chamber 31 for housing a wafer 51. Typically thewafer 51 resides atop a support (or chuck 33). A heater 34 is alsocoupled to the chuck 33 to control temperature of the chuck 33 and thewafer 51 for deposition. Processing chemicals are combined with acarrier gas upstream and introduced into the chamber 31 through a gasdistributor 35 located at upstream end of the chamber 31. A vacuum pump36 and a throttling valve 37 are located at the downstream end to drawand regulate the gas flow across the wafer surface.

A manifold 38 combines the various processing chemicals with the carriergas and the carrier gas/chemical combination is directed to a remoteplasma forming zone 39 for forming plasma when necessary. A variety oftechniques for combining gasses and forming plasma may be utilized,including adapting techniques known in the art. The remotely formedplasma 39, need not necessarily be placed in-line as shown in the FIG.7. The carrier gas is then fed through the gas distributor 35 and theninto the chamber 31.

The manifold 38 has two inlets for the introduction of chemicals, aswell as for the carrier gas. The carrier gas is typically an inert gas,such as nitrogen. Additional inlets can be readily coupled to themanifold 38. In the example apparatus 30, the manifold is a gasswitching manifold to switch in the various chemicals into the flowstream of the carrier gas. Chemical A in the example pertains to thefirst precursor and chemical B pertains to the second precursor forperforming ALD for a two precursor process. Chemical selection manifolds40 and 41, comprised of a number of regulated valves, provide for theselection of chemicals that may be used as precursors A and B,respectively. Inlet valves 42 and 43 respectively regulate introductionof the precursor chemistries A and B into the manifold 38. The valves42, 43 are typically pulsed open for a certain duration pulse time tocontrol the timing and amount of chemical insertion into the carrierstream.

The particular manifold 38 has a split flow stream of carrier gas. Inthe diagram, the right flow stream is used to carry chemical A whenchemical A is introduced into the carrier gas flow stream. Likewise theleft flow path of carrier gas is used for chemical B when chemical B isintroduced into the left flow path. It is appreciated that the splitflow design of the carrier gas may have additional flow path. Thecontinuous flow of the carrier gas through the split path ensures that acontinuous flow is available whenever chemical A or chemical B isintroduced into the manifold. Furthermore, when the chemicals are notintroduced into the manifold the continuous flow of the carrier gasensures that the reactor is purged of previous precursors.

In one particular application of the ALD reactor, the carrier gascontinuously flows, while chemical A and chemical B are alternativelypulsed into the manifold to pulse the first and second precursors intothe reactor chamber. The continuous flowing of the carrier gas betweenthe pulsed opening of the valves 42 and 43 ensures that the reactor ispurged of the previous precursor before the next precursor is introducedto the reactor 31. When pre-treatment is desired to initiate the growthof films on different substrates, pretreatment chemicals may beintroduced into the manifold 38 through either valves 42, 43 or anothervalve.

It is appreciated that a number of techniques are available to removethe PS layer overlying the FM layer. In one technique, a cluster toolprovides a separate chamber for etching the PS layer and a separatelayer for ALD of the dielectric layer. Since both chambers are withinthe non-ambient environment of the tool, the uncovered FM layer is notexposed (at least considerably limited in exposure) to the ambient.

In another technique, the ALD chamber may also provide both processingfunctions. Prior to ALD, an etchant may be introduced into the reactor,typically through the manifold 38 of the example system of FIG. 7, sothat the etchant may remove the PS layer prior to ALD. The carrier gaswould purge the etchant before performing ALD. It is appreciated thatother designs may be readily implemented to utilize the same reactorchamber for both removing the PS layer and depositing the dielectriclayer by ALD.

Thus, an apparatus and method to perform fully integrated ALD to deposita dielectric layer over a ferromagnetic layer to form a FM/I junction isdescribed. The technique may be used to fabricate a FM/I/FM device on aceramic substrate. Other materials may be used for the base substrate(or wafer). The present invention provides integration solutionthroughout the necessary processes of forming the bottom FM layer andforming a subsequent dielectric layer above the FM layer without (or atleast minimized) oxidization or contamination of the FM/I interface.Furthermore, it is to be noted that the technique described above may beapplied to form devices other than ferromagnetic memory storage devices.Other structures employing a ferromagnetic insulator tunneling junctioncan be readily manufactured utilizing various embodiments of theinvention.

I claim:
 1. A method comprising: depositing a first ferromagnetic layeronto an underlying material; depositing a protective sacrificial layerabove the first ferromagnetic layer without exposing the firstferromagnetic layer to ambient environment, the protective sacrificiallayer being removal selective over the first ferromagnetic layer;exposing the protective sacrificial layer to an oxidizing ambient toundergo photolithographic and material removal processes that form adefined stacked structure by pattern delineating the first ferromagneticlayer; placing the material into a vacuum environment prior to removingthe protective sacrificial layer; removing the protective sacrificiallayer by a selective process to expose the first ferromagnetic layerunder vacuum; and depositing a dielectric layer over the firstferromagnetic layer by atomic layer deposition in the vacuumenvironment.
 2. The method of claim 1 further comprising depositing asecond ferromagnetic layer above the deposited dielectric layer.
 3. Themethod of claim 1 further comprising depositing a second protectivesacrificial layer above the dielectric layer by atomic layer depositionwithout exposing the dielectric layer to the ambient environment,patterning the dielectric layer in an oxidizing ambient, and placing thematerial into a non-ambient environment to remove the second protectivesacrificial layer and to deposit a second ferromagnetic layer above thedielectric layer.
 4. The method of claim 2 further comprising formingferromagnetic-dielectric-ferromagnetic tunneling junctions on thematerial by forming the first ferromagnetic, dielectric and secondferromagnetic layers.
 5. The method of claim 1 wherein said depositingof the dielectric layer deposits the dielectric layer to a thickness inan approximate range of 5-20 Angstroms.
 6. The method of claim 1 whereinsaid removing the protective sacrificial layer includes removing byisotropic dry etch.
 7. The method of claim 1 wherein said removing theprotective sacrificial layer includes removing by isotropic dry etchusing fluorine chemistry.
 8. The method of claim 1 wherein saiddepositing the dielectric layer includes depositing Al₂O₃.
 9. The methodof claim 1 wherein said depositing the dielectric layer includesdepositing AIN.
 10. The method of claim 1 further comprising activatinga surface of the first ferromagnetic layer to enhance surface activationto perform atomic layer deposition prior to depositing the dielectriclayer.
 11. A method of fabricating aferromagnetic-dielectric-ferromagnetic tunneling device comprising:depositing a first ferromagnetic layer onto a substrate; depositing aprotective sacrificial layer above the first ferromagnetic layer withoutexposing the first ferromagnetic layer to ambient environment, theprotective sacrificial layer being etch selective over the firstferromagnetic layer; patterning the first ferromagnetic layer and theoverlying protective sacrificial layer to form a patterned stack in anoxidizing ambient; placing the substrate into an atomic layer depositionchamber; removing the protective sacrificial layer in the atomic layerdeposition environment to expose the first ferromagnetic layer;depositing a dielectric layer over the first ferromagnetic layer byatomic layer deposition; and depositing a second ferromagnetic layerover the dielectric layer.
 12. The method of claim 14 wherein saidremoving the protective sacrificial layer includes removing by isotropicdry etch.
 13. The method of claim 14 wherein said removing theprotective sacrificial layer includes removing by isotropic dry etchusing fluorine chemistry.
 14. The method of claim 14 wherein saiddepositing the protective sacrificial layer includes depositing W orWNx.
 15. The method of claim 14 wherein said depositing the protectivesacrificial layer includes depositing Si or SiNx.
 16. The method ofclaim 14 wherein said depositing the dielectric layer includesdepositing Al₂O₃.
 17. The method of claim 14 wherein said depositing thedielectric layer includes depositing AlN.
 18. The method of claim 14wherein said depositing of the dielectric layer deposits the dielectriclayer to a thickness in an approximate range of 5-20 Angstroms.
 19. Themethod of claim 14 further comprising depositing a second protectivesacrificial layer above the dielectric layer by atomic layer depositionwithout exposing the dielectric layer to the ambient environment,patterning the dielectric layer in an oxidizing environment, andremoving the second protective sacrificial layer before deposition ofthe second ferromagnetic layer without exposing the underlyingdielectric layer to the ambient environment to deposit the secondferromagnetic layer.
 20. The method of claim 14 further comprisingactivating a surface of the first ferromagnetic layer to enhance surfaceactivation to perform atomic layer deposition of the dielectric layer.21. The method of claim 23 wherein said activating further includesactivating by exposure to NH₃/H₂ plasma to remove surface fluorine andfacilitate NH_(x), species termination.